Erected in
times of crisis in order to ensure that those passing through pass certain
criteria. Rarer than
Army Checkpoints or the more general
Military Checkpoint.
Popular American media would have us believe these are only seen in Eastern European Cold war countries, or Russia itself, and in the Western World at times of extreme crisis (Martial Law, for example).
In fact, the only thing that differentiates a checkpoint and getting stopped by the police is a good reason be stopped. In the United Kingdom, it is now permissible for the police to stop civilians without reason. This is the thin end of the wedge, or a sensible crime/drug/drink driving deterrent, depending (yet again) on your point of view.